diff --git a/lib/pronto/comment.rb b/lib/pronto/comment.rb
index 69a56dfa..52373edb 100644
--- a/lib/pronto/comment.rb
+++ b/lib/pronto/comment.rb
@@ -1,5 +1,5 @@
 module Pronto
-  Comment = Struct.new(:sha, :body, :path, :position) do
+  Comment = Struct.new(:sha, :body, :path, :position, :id) do
     def ==(other)
       position == other.position &&
         path == other.path &&
diff --git a/lib/pronto/formatter/git_formatter.rb b/lib/pronto/formatter/git_formatter.rb
index 6a781dfe..5e734b56 100644
--- a/lib/pronto/formatter/git_formatter.rb
+++ b/lib/pronto/formatter/git_formatter.rb
@@ -6,8 +6,10 @@ def format(messages, repo, patches)
         existing = existing_comments(messages, client, repo)
         comments = new_comments(messages, patches)
         additions = remove_duplicate_comments(existing, comments)
+        outdated_comments = existing.reject { |key, _| comments.key?(key) }.values.flatten
+        remove_outdated_comments(client, outdated_comments) if respond_to?(:remove_outdated_comments)
         submit_comments(client, additions)
-        
+
         approve_pull_request(comments.count, additions.count, client) if defined?(self.approve_pull_request)
 
         "#{additions.count} Pronto messages posted to #{pretty_name} (#{existing.count} existing)"
diff --git a/lib/pronto/formatter/github_pull_request_formatter.rb b/lib/pronto/formatter/github_pull_request_formatter.rb
index e0778b10..4f8b085b 100644
--- a/lib/pronto/formatter/github_pull_request_formatter.rb
+++ b/lib/pronto/formatter/github_pull_request_formatter.rb
@@ -16,6 +16,14 @@ def pretty_name
       def line_number(message, _)
         message.line&.new_lineno
       end
+
+      def remove_outdated_comments(client, outdated_comments)
+        outdated_comments.each do |comment|
+          client.delete_comment(comment)
+        end
+      rescue Octokit::UnprocessableEntity, HTTParty::Error => e
+        warn "Failed to delete: #{e.message}"
+      end
     end
   end
 end
diff --git a/lib/pronto/github.rb b/lib/pronto/github.rb
index dc702cea..5027c25b 100644
--- a/lib/pronto/github.rb
+++ b/lib/pronto/github.rb
@@ -11,7 +11,7 @@ def pull_comments(sha)
       @comment_cache["#{pull_id}/#{sha}"] ||= begin
         client.pull_comments(slug, pull_id).map do |comment|
           Comment.new(
-            sha, comment.body, comment.path, comment.line || comment.original_line
+            sha, comment.body, comment.path, comment.line || comment.original_line, comment.id
           )
         end
       end
@@ -66,6 +66,10 @@ def create_commit_status(status)
                            description: status.description)
     end
 
+    def delete_comment(comment)
+      client.delete_pull_comment(slug, comment.id)
+    end
+
     private
 
     def create_pull_request_review(comments)
diff --git a/spec/pronto/formatter/github_pull_request_formatter_spec.rb b/spec/pronto/formatter/github_pull_request_formatter_spec.rb
index bf2689ac..55b13c3f 100644
--- a/spec/pronto/formatter/github_pull_request_formatter_spec.rb
+++ b/spec/pronto/formatter/github_pull_request_formatter_spec.rb
@@ -25,7 +25,7 @@ module Formatter
           octokit_client
             .stub(:pull_comments)
             .once
-            .and_return([double(body: 'a comment', path: 'a/path', line: 5)])
+            .and_return([double(body: 'a comment', path: 'a/path', line: 5, id: 1_881_471_822)])
         end
 
         specify do
@@ -33,6 +33,8 @@ module Formatter
             .should_receive(:create_pull_comment)
             .once
 
+          octokit_client.should_receive(:delete_pull_comment).with(nil, 1_881_471_822).and_return(true)
+
           subject
         end
 
@@ -43,7 +45,7 @@ module Formatter
 
           specify do
             octokit_client.should_receive(:pull_comments).and_return(
-              [double(body: 'existed', path: 'path/to', line: line.new_lineno)]
+              [double(body: 'existed', path: 'path/to', line: line.new_lineno, id: 1_881_471_822)]
             )
 
             octokit_client.should_not_receive(:create_pull_comment)
@@ -59,7 +61,7 @@ module Formatter
 
           specify do
             octokit_client.should_receive(:pull_comments).and_return(
-              [double(body: 'existed', path: 'path/to', line: line.new_lineno)]
+              [double(body: 'existed', path: 'path/to', line: line.new_lineno, id: 1_881_471_822)]
             )
 
             octokit_client.should_receive(:create_pull_comment).once
@@ -92,6 +94,8 @@ module Formatter
               .should_receive(:create_pull_comment)
               .and_raise(error)
 
+            octokit_client.should_receive(:delete_pull_comment).with(nil, 1_881_471_822).and_return(true)
+
             $stderr.should_receive(:puts) do |line|
               line.should =~ /Failed to post/
               line.should =~ /Validation Failed/
diff --git a/spec/pronto/formatter/github_pull_request_review_formatter_spec.rb b/spec/pronto/formatter/github_pull_request_review_formatter_spec.rb
index c01a37ef..c80a7bca 100644
--- a/spec/pronto/formatter/github_pull_request_review_formatter_spec.rb
+++ b/spec/pronto/formatter/github_pull_request_review_formatter_spec.rb
@@ -33,7 +33,7 @@ module Formatter
 
           specify do
             octokit_client.should_receive(:pull_comments).and_return(
-              [double(body: 'existed', path: 'path/to', line: line.new_lineno)]
+              [double(body: 'existed', path: 'path/to', line: line.new_lineno, id: 1_881_471_822)]
             )
 
             octokit_client.should_not_receive(:create_pull_request_review)
@@ -49,7 +49,7 @@ module Formatter
 
           specify do
             octokit_client.should_receive(:pull_comments).and_return(
-              [double(body: 'existed', path: 'path/to', line: line.new_lineno)]
+              [double(body: 'existed', path: 'path/to', line: line.new_lineno, id: 1_881_471_822)]
             )
 
             octokit_client.should_receive(:create_pull_request_review).once
diff --git a/spec/pronto/github_spec.rb b/spec/pronto/github_spec.rb
index 0991c7c7..7f4344fd 100644
--- a/spec/pronto/github_spec.rb
+++ b/spec/pronto/github_spec.rb
@@ -5,7 +5,7 @@ module Pronto
     let(:ssh_remote_urls) { ["git@github.com:#{github_slug}.git"] }
     let(:github_slug) { 'prontolabs/pronto' }
     let(:sha) { '61e4bef' }
-    let(:comment) { double(body: 'note', path: 'path', line: 1, position: 1) }
+    let(:comment) { double(body: 'note', path: 'path', line: 1, position: 1, id: 1_881_471_822) }
     let(:empty_client_options) do
       {
         event: 'COMMENT'